As the world population and industry grow, the demand for energy has risen. For most of the last two centuries the extra demand was met mainly by burning fossil fuels, first coal and then oil and natural gas. Looking at data over many years shows trends: some resources are used more, and others less.
In the UK the use of coal has fallen sharply, and natural gas took over much of its place. Over recent decades wind and solar have grown quickly, and they supply a much larger share of electricity than they once did. Total energy use per person has also fallen in the UK as homes, vehicles and appliances have become more efficient. As more people switch to electric vehicles, demand shifts from oil to electricity.
Several reasons explain these trends. Burning fossil fuels releases carbon dioxide into the atmosphere, and concern about climate change leads governments to set targets and give support for renewable energy. The cost of building wind and solar has fallen. Fossil fuel reserves are limited, and countries want a supply they control. Coal also causes more air pollution than other fuels. Against this, new power stations and wind farms take years to build, and the weather affects how much wind and solar can deliver.
You may be asked to work with data. The percentage share of a source is the part divided by the total, multiplied by 100. For example, 90 TWh from renewables out of a total of 300 TWh is 90 ÷ 300 × 100 = 30%. Unit conversions use ratios too: 1 kW h = 3 600 000 J, so energy in kW h is multiplied by 3 600 000 to give joules. A rate is an amount divided by time, for example power in watts is joules per second.